Should Pregnant Women Be Tested for Hypothyroidism?

LOS ANGELES — Recent evidence suggests many hypothyroid pregnant women are not identified as such by their medical providers, to the detriment of the mother and child, Dr. Jorge H. Mestman said at a meeting of the Obstetrical and Gynecological Assembly of Southern California.

The experts cannot reach a consensus on whether pregnant women should be routinely screened for thyroid disease, but even hypothyroidism that is subclinical prior to pregnancy appears to have a severe, negative impact on the pregnancy and child, said Dr. Mestman, director of the Center for Diabetes and Metabolic Diseases at the University of Southern California, Los Angeles.

“There is no agreement,” Dr. Mestman said. “You have to decide in your office if you are going to check everybody for thyroid disease in the same way as for diabetes.”

One important new study might not have been seen by many in the obstetrics community because it was published in an endocrinology journal, he noted. The investigators attempted to see if the strategy of identifying women at high risk of thyroid disease (those with a personal or family history) and performing thyroid testing only in those women would pick up most cases.

They enrolled 1,560 pregnant women on their first prenatal visit, and tested their thyroid function and determined whether they had thyroid antibodies. Forty were found to have elevated thyroid-stimulating hormone (TSH) levels. Of those, 70% were in the high-risk group due to a personal history of thyroid or autoimmune disease, or a family history of thyroid disease.

But 12 of the 40 had no history, and would not, therefore have received testing according to the protocol being examined by the study (J. Clin. Endocrinol. Metab. 2007;92:203–7).

Chronic thyroiditis occurs in between 5% and 20% of women of child-bearing age, Dr. Mestman said. Subclinical hypothyroidism—a normal thyroxine (T4) level but an elevated TSH—may have an incidence of 2%.

Many studies have shown that hypothyroidism, even subclinical hypothyroidism, is associated with a two- to fivefold higher risk of miscarriage and premature delivery.

One study found that at age 7–9 years, children of mothers who were hypothyroid in pregnancy had a mean IQ 4 points lower than controls. The mean IQ of children of women who were hypothyroid during pregnancy and not treated was 7 points less (N. Engl. J. Med. 1999;341:549–55).

The detrimental effects of hypothyroidism presumably occur because the mother produces all the thyroid hormone for her fetus during the first trimester at least, and fetal brains have been shown to have thyroid hormone receptors.

During the first trimester, T4 levels need to increase by 50%, which is why women who may be subclinical before conception can run into trouble. They cannot compensate for the increased demand.

By the second and third trimester, T4 levels return to normal; however, some women who become hypothyroid during the first trimester will become hypothyroid again after delivery. Those women will become hyperthyroid for the first 3 months after delivery, and then hypothyroid for approximately another 6 months. Of those, about 30% will become clinically hypothyroid within 5 years. All of these women should be followed for thyroid function after their pregnancy, Dr. Mestman said. The pattern can occur even after spontaneous abortion.

Treatment prevents pregnancy complications, Dr. Mestman said. In a series of 88 hypothyroid women, the pregnancy complication rate of those who never became euthyroid during their pregnancy was 32% (6 of 19 patients), compared with 17% in those women who became euthyroid but only after 20 weeks' gestation (7 of 42), and 5% in those who became euthyroid before 20 weeks (1 of 21).

One of the tragedies observed in that series concerned the 30% already on levothyroxine prior to their pregnancy, Dr. Mestman said. Some were told to stop all medications when they became pregnant and they stopped their thyroid medication.

“This is a very common practice in many, many places,” he said.

Another, more recent study also looked at the pregnancy complication rate in women who were euthyroid but who had thyroid peroxidase antibodies. They treated half of a group of 115 antibody-positive women with levothyroxine, and compared those women with 869 pregnant women who were antibody negative.

The treated antibody-positive women had a miscarriage rate of 3%, similar to the rate in the control group, 2%. But the untreated antibody-positive women had a rate of 14%. The treated women had a premature delivery rate of 7%, similar to the 8% for the control group. That compared with a rate of 22% for the untreated women.

Given those findings, Dr. Mestman recommended that pregnant, antibody-positive euthyroid women should be treated. The treatment should include a prenatal vitamin with 150 mcg of iodine. They should have TSH and T4 levels monitored every 4–6 weeks during the first 20 weeks of pregnancy. After 20 weeks, they should have their TSH and T4 measured once at 28 weeks and should take 50–75 mcg a day of levothyroxine. If the patient is already on levothyroxine, the dose should be increased by 25 mcg.

LOS ANGELES — Recent evidence suggests many hypothyroid pregnant women are not identified as such by their medical providers, to the detriment of the mother and child, Dr. Jorge H. Mestman said at a meeting of the Obstetrical and Gynecological Assembly of Southern California.

The experts cannot reach a consensus on whether pregnant women should be routinely screened for thyroid disease, but even hypothyroidism that is subclinical prior to pregnancy appears to have a severe, negative impact on the pregnancy and child, said Dr. Mestman, director of the Center for Diabetes and Metabolic Diseases at the University of Southern California, Los Angeles.

“There is no agreement,” Dr. Mestman said. “You have to decide in your office if you are going to check everybody for thyroid disease in the same way as for diabetes.”

One important new study might not have been seen by many in the obstetrics community because it was published in an endocrinology journal, he noted. The investigators attempted to see if the strategy of identifying women at high risk of thyroid disease (those with a personal or family history) and performing thyroid testing only in those women would pick up most cases.

They enrolled 1,560 pregnant women on their first prenatal visit, and tested their thyroid function and determined whether they had thyroid antibodies. Forty were found to have elevated thyroid-stimulating hormone (TSH) levels. Of those, 70% were in the high-risk group due to a personal history of thyroid or autoimmune disease, or a family history of thyroid disease.

But 12 of the 40 had no history, and would not, therefore have received testing according to the protocol being examined by the study (J. Clin. Endocrinol. Metab. 2007;92:203–7).

Chronic thyroiditis occurs in between 5% and 20% of women of child-bearing age, Dr. Mestman said. Subclinical hypothyroidism—a normal thyroxine (T4) level but an elevated TSH—may have an incidence of 2%.

Many studies have shown that hypothyroidism, even subclinical hypothyroidism, is associated with a two- to fivefold higher risk of miscarriage and premature delivery.

One study found that at age 7–9 years, children of mothers who were hypothyroid in pregnancy had a mean IQ 4 points lower than controls. The mean IQ of children of women who were hypothyroid during pregnancy and not treated was 7 points less (N. Engl. J. Med. 1999;341:549–55).

The detrimental effects of hypothyroidism presumably occur because the mother produces all the thyroid hormone for her fetus during the first trimester at least, and fetal brains have been shown to have thyroid hormone receptors.

During the first trimester, T4 levels need to increase by 50%, which is why women who may be subclinical before conception can run into trouble. They cannot compensate for the increased demand.

By the second and third trimester, T4 levels return to normal; however, some women who become hypothyroid during the first trimester will become hypothyroid again after delivery. Those women will become hyperthyroid for the first 3 months after delivery, and then hypothyroid for approximately another 6 months. Of those, about 30% will become clinically hypothyroid within 5 years. All of these women should be followed for thyroid function after their pregnancy, Dr. Mestman said. The pattern can occur even after spontaneous abortion.

Treatment prevents pregnancy complications, Dr. Mestman said. In a series of 88 hypothyroid women, the pregnancy complication rate of those who never became euthyroid during their pregnancy was 32% (6 of 19 patients), compared with 17% in those women who became euthyroid but only after 20 weeks' gestation (7 of 42), and 5% in those who became euthyroid before 20 weeks (1 of 21).

One of the tragedies observed in that series concerned the 30% already on levothyroxine prior to their pregnancy, Dr. Mestman said. Some were told to stop all medications when they became pregnant and they stopped their thyroid medication.

“This is a very common practice in many, many places,” he said.

Another, more recent study also looked at the pregnancy complication rate in women who were euthyroid but who had thyroid peroxidase antibodies. They treated half of a group of 115 antibody-positive women with levothyroxine, and compared those women with 869 pregnant women who were antibody negative.

The treated antibody-positive women had a miscarriage rate of 3%, similar to the rate in the control group, 2%. But the untreated antibody-positive women had a rate of 14%. The treated women had a premature delivery rate of 7%, similar to the 8% for the control group. That compared with a rate of 22% for the untreated women.

Given those findings, Dr. Mestman recommended that pregnant, antibody-positive euthyroid women should be treated. The treatment should include a prenatal vitamin with 150 mcg of iodine. They should have TSH and T4 levels monitored every 4–6 weeks during the first 20 weeks of pregnancy. After 20 weeks, they should have their TSH and T4 measured once at 28 weeks and should take 50–75 mcg a day of levothyroxine. If the patient is already on levothyroxine, the dose should be increased by 25 mcg.

LOS ANGELES — Recent evidence suggests many hypothyroid pregnant women are not identified as such by their medical providers, to the detriment of the mother and child, Dr. Jorge H. Mestman said at a meeting of the Obstetrical and Gynecological Assembly of Southern California.

The experts cannot reach a consensus on whether pregnant women should be routinely screened for thyroid disease, but even hypothyroidism that is subclinical prior to pregnancy appears to have a severe, negative impact on the pregnancy and child, said Dr. Mestman, director of the Center for Diabetes and Metabolic Diseases at the University of Southern California, Los Angeles.

“There is no agreement,” Dr. Mestman said. “You have to decide in your office if you are going to check everybody for thyroid disease in the same way as for diabetes.”

One important new study might not have been seen by many in the obstetrics community because it was published in an endocrinology journal, he noted. The investigators attempted to see if the strategy of identifying women at high risk of thyroid disease (those with a personal or family history) and performing thyroid testing only in those women would pick up most cases.

They enrolled 1,560 pregnant women on their first prenatal visit, and tested their thyroid function and determined whether they had thyroid antibodies. Forty were found to have elevated thyroid-stimulating hormone (TSH) levels. Of those, 70% were in the high-risk group due to a personal history of thyroid or autoimmune disease, or a family history of thyroid disease.

But 12 of the 40 had no history, and would not, therefore have received testing according to the protocol being examined by the study (J. Clin. Endocrinol. Metab. 2007;92:203–7).

Chronic thyroiditis occurs in between 5% and 20% of women of child-bearing age, Dr. Mestman said. Subclinical hypothyroidism—a normal thyroxine (T4) level but an elevated TSH—may have an incidence of 2%.

Many studies have shown that hypothyroidism, even subclinical hypothyroidism, is associated with a two- to fivefold higher risk of miscarriage and premature delivery.

One study found that at age 7–9 years, children of mothers who were hypothyroid in pregnancy had a mean IQ 4 points lower than controls. The mean IQ of children of women who were hypothyroid during pregnancy and not treated was 7 points less (N. Engl. J. Med. 1999;341:549–55).

The detrimental effects of hypothyroidism presumably occur because the mother produces all the thyroid hormone for her fetus during the first trimester at least, and fetal brains have been shown to have thyroid hormone receptors.

During the first trimester, T4 levels need to increase by 50%, which is why women who may be subclinical before conception can run into trouble. They cannot compensate for the increased demand.

By the second and third trimester, T4 levels return to normal; however, some women who become hypothyroid during the first trimester will become hypothyroid again after delivery. Those women will become hyperthyroid for the first 3 months after delivery, and then hypothyroid for approximately another 6 months. Of those, about 30% will become clinically hypothyroid within 5 years. All of these women should be followed for thyroid function after their pregnancy, Dr. Mestman said. The pattern can occur even after spontaneous abortion.

Treatment prevents pregnancy complications, Dr. Mestman said. In a series of 88 hypothyroid women, the pregnancy complication rate of those who never became euthyroid during their pregnancy was 32% (6 of 19 patients), compared with 17% in those women who became euthyroid but only after 20 weeks' gestation (7 of 42), and 5% in those who became euthyroid before 20 weeks (1 of 21).

One of the tragedies observed in that series concerned the 30% already on levothyroxine prior to their pregnancy, Dr. Mestman said. Some were told to stop all medications when they became pregnant and they stopped their thyroid medication.

“This is a very common practice in many, many places,” he said.

Another, more recent study also looked at the pregnancy complication rate in women who were euthyroid but who had thyroid peroxidase antibodies. They treated half of a group of 115 antibody-positive women with levothyroxine, and compared those women with 869 pregnant women who were antibody negative.

The treated antibody-positive women had a miscarriage rate of 3%, similar to the rate in the control group, 2%. But the untreated antibody-positive women had a rate of 14%. The treated women had a premature delivery rate of 7%, similar to the 8% for the control group. That compared with a rate of 22% for the untreated women.

Given those findings, Dr. Mestman recommended that pregnant, antibody-positive euthyroid women should be treated. The treatment should include a prenatal vitamin with 150 mcg of iodine. They should have TSH and T4 levels monitored every 4–6 weeks during the first 20 weeks of pregnancy. After 20 weeks, they should have their TSH and T4 measured once at 28 weeks and should take 50–75 mcg a day of levothyroxine. If the patient is already on levothyroxine, the dose should be increased by 25 mcg.